The invention relates to matt and scratch-resistant, amorphous to crystalline films of thermoplastics which are filled with glass spheres.
To manufacture matted films it is customary to convert thermoplastic moulding compositions filled with fillers, for example with titanium dioxide, into films. These films have the disadvantage that the surfaces can be scratched relatively easily, which restricts the range of applications, for example the use as the top layer in a veneering material for furniture or doors.
Thermoplastic moulding compositions which contain glass fibres and/or glass spheres as a reinforcing and filling material are also known. These moulding materials are used for the manufacture of injection mouldings. For example, W. Knoss, Glaskugeln ("Glass Spheres", Industrieanzeiger 93, No. 72, 1971, 1835-1838 and J. Ritter, Applied Polymer Symposium No. 15, 1971, 239-261 describe the general properties of such injection mouldings of polyamides filled with glass spheres and also mention that polyesters can be used as the plastics. Japanese Published Patent 73/05,257 describes moulding compositions of polyethylene terephthalate, reinforced with glass fibres and glass spheres, which are suitable for use in injection moulding, and German 2,206,804 describes polybutylene terephthalates which contain either glass fibres or glass spheres and can also be used for the manufacture of injection mouldings. However, none of these publications mentions that high quality films with certain surface properties can be manufactured from thermoplastic moulding compositions reinforced with glass spheres. Furthermore, so-called "reflecting films", which consist of a thermoplastic and of which the surface is coated with glass spheres, are already known. Since the glass spheres are glued to these films, the scratch resistance of the films is only low.
The German Offenlegungsschrift 1,504,522 describes films of thermoplastics which contain solid particles such as calcium carbonate as a filler. These films are prepared by melt-extrusion and after cooling by stretching them at a temperature above the glass transition temperature, but below a temperature of the polymer being in the melt-fluid state. The main purpose of these matted films is that on the surface of said films it can be written and that the written lines cannot be lightly wiped off. It was found that a full surface mattness of these films is only obtained in using other than glass spheres as a filler. It was also found that with the other fillers, e.g., calcium carbonate, the desired mattness of the films is only obtained when the melt-extruded film is stretched above the glass transition temperature and below the temperature of the polymer melt and that these films have a poor scratch-resistance. It was further found that in embossing these films the desired structures are insufficiently portrayed.
Both the process and the product made therefrom of German Pat. No. 1,504,522 differ significantly from the instant process and product. German Pat. No. 1,504,522 teaches a process to prepare a sheet or film of a thermoplastic composition containing a thermoplastic and a filler such as mica, glass, titanium dioxide or particularly calcium carbonate which comprises (a) extruding the thermoplastic composition in a conventional manner; (b) taking up the sheet or film at a temperature below the glass transition temperature of the thermoplastic with the sheet or film being obtained in a relatively unstretched state and with a smooth surface having no projections or domes arising therefrom as seen by FIG. 1 of German Pat. No. 1,504,522, and (c) stretching in either an integrated third step or in an entirely separate operation isolated from the above extruding and taking up steps in both location and/or time by reheating the sheet or film to a temperature above the glass transition temperature of the thermoplastic and then uniaxially or biaxially orienting said sheet or film to cause only then the surface of the sheet or film to exhibit the form projections (7) seen in FIG. 2 of German Pat. No. 1,504,522. Still further stretching results in the structure of FIG. 3 of said German reference wherein the sheet or film contains voids and pore spaces.
These stretched sheets or films of German Pat. No. 1,504,522 can be highly oriented and are of high crystallinity.
It is an object of this invention to provide matted and scratch resistant films or sheet which can be more easily embossed in fully portraying the desired structure.
Accordingly, the product of the present invention is a matted and scratch-resistant, amorphous to crystalline sheet or film of a film-forming thermoplastic and a filler in an amount of 2 to 25% by weight, based on the weight of polymer, said filler consisting of glass spheres of size from 0.5 to 75.mu., preferably 0.5 to 50.mu., uniformly distributed therein, said sheet or film having been extruded and taken up in an integrated two-step process whereby said sheet or film was stretched in the melt-fluid state at a decreasing temperature gradient between the temperature of the melt extrusion means and the temperature of the take-up means, and said sheet or film having a surface characterized by projecting domes of the glass spheres which are still completely covered by thermoplastic.
Preferably, the films or sheets contain 5 to 15% by weight, especially 5.5 to 12% by weight, of glass spheres and most preferably the average size of the glass spheres is 0.5 to 20.mu..
The films or sheets are manufactured by means of known devices from moulding compositions in which the glass spheres are uniformly distrubuted in the thermoplastic. Suitable thermoplastics are all film-forming polymers. Plastics from which very thin films can be manufactured are preferred. Particularly suitable thermoplastics for the manufacture of the films or sheets according to the invention have proved to be polyalkylene terephthalates, especially polyethylene terephthalates, and polyamides, especially polyamide 6, polyamide 6,6, polyamide 11 and polyamide 12.
The plastic moulding compositions can contain customary further additives, such as, for example, fillers, matting agents, such as micro-mica, titanium dioxide or suitable colorants. As a further matting additive, preferably 0.01 to 5%, and especially 0.1 to 2% by weight of micro-mica is admixed to the moulding composition. Furthermore, flame-proofing substances, for example tetrabromophthalic anhydride or decarbromodiphenyl can be present, optionally together with antimony trioxide. In order to prevent the films or sheets according to the invention sticking to the surfaces of the tools during manufacture or during further processing, known mould release agents, such as, for example, polyethylene, waxes or silicones, can be added to the moulding compositions.
The content and especially the size of the glass spheres depends on the film thickness and on the desired mattness. It has proved desirable that the average diameter of the glass spheres should be less than half the film thickness. To assist the flawless embedding of the glass spheres in the plastic matrix, an adhesion-promoting substance can be used in addition. In that case, the adhesion promoter can be added together with the glass spheres to the plastic, or can be applied to the surface of the glass spheres before these are mixed with the plastic. Adhesion promoters which can be used are in particular the compositions described as "sizes" which are known for binding glass fibres or glass particles to plastics in which they are embedded.
The manufacture of the films according to the invention is carried out with devices known for the purpose. To produce the films, the thermoplastic moulding compositions, which contain, uniformly distributed, 2 to 25% by weight of glass spheres of size from 0.5 to 75.mu., are converted to a layer by extrusion from a slit die or circular die and stretched, while still in the melt-fluid state, to the point that the surface structure of the films or sheets is formed by projecting domes of the glass spheres, which are still completely covered by plastic.
An integrated two-step, continuous process for the manufacture of a matted and scratch-resistant, amorphous to crystalline sheet or film of a film-forming thermoplastic and a filler in an amount of 2 to 25% by weight, based on the weight of polymer, comprises
extruding from an extrusion means, at the melt extrusion temperature of the thermoplastic, a thermoplastic composition containing a thermoplastic and filler, said filler consisting of glass spheres of size from 0.5 to 75.mu., uniformly distributed therein, and PA1 taking-up said sheet or film on a take-up means at a temperature below the glass transition temperature of said thermoplastic, said take-up means being operated at such a rate as to cause said sheet or film to be stretched in the melt-fluid state at a decreasing temperature gradient between the temperature of the melt extrusion means and the temperature of the take-up means and to cause the surface of said sheet or film to be characterized by projecting domes of the glass spheres which are still completely covered by thermoplastic.
The degree of crystallinity of the films or sheets according to the invention can be controlled by the rate of cooling after extrusion. If rapid cooling is used, amorphous to slightly crystalline, translucent films or sheets are obtained, whilst on slower cooling predominantly more crystalline products are obtained. The amorphous to slightly crystalline films or sheets according to the invention can also be converted into films of high degree of crystallinity by a subsequent heat treatment. The amorphous to slightly crystalline films or sheets can also first be warmed and then be stretched biaxially, whereby crystalline films or sheets of increased strength are obtained.
The degree of crystallinity and of orientation in polymeric pellicles can be conveniently ascertained by X-ray diffraction techniques (Charles Tanford, Physical Chemistry of Macromolecules, John Wiley & Sons, New York, 1961, pages 37-43).
X-ray diffraction of a typical film made by the instant process would show it to be of relatively low crystallinity and low orientation. Heating such a film would convert it to high crystalinity with unchanged (low) orientation as seen by X-ray diffraction.
By contrast, an X-ray diffraction diagram of a typical uniaxially (or biaxially) oriented film stretched by the process (in the third step) of German 1,504,522 would indicate a highly crystalline film with high (or very discernible) orientation.
Thus X-ray diffraction provides another independent indication of the differences between the instant process and product compared to those of German Pat. No. 1,504,522.
The scratch-resistant film material according to the invention can be laminated to other materials, for example wood, glass, metal or other plastics, and the customary adhesion promotors can be used for this purpose. Depending on the nature of the materials, an appropriate adhesion promoter will be employed, say an adhesion promoter which can be heat-activated and which has beforehand been applied either to the film material according to the invention or to the material to which the latter is to be laminated. In the case of lamination of the films according to the invention to other plastic films, preferably, for example, of PVC, polyethylene, chlorinated polyethylene, ethylene/vinyl acetate, polystyrene or copolymers of, for example, acrylonitrile, butadiene and styrene, and alternative procedure is to extrude the films simultaneously and bond them to one another whilst still in the molten state.
The film material according to the invention can be embossed in order to apply a pattern, without changing the surface structure consisting of domes (of the spheres). Accordingly, the matting and the scratch resistance are retained even after the embossing process. The embossing can also be carried out with laminated films of the material according to the invention and other plastics. Here, the embossing is also formed on the lower film if its softening point is lower than that of the material according to the invention.
A preferred field of use for the film material according to the invention is the manufacture or veneer materials, for example for furniture manufacture, for doors or for wall claddings. For this purposes, it is possible to use the films according to the invention, provided with a veneer pattern, or to use embossed laminated films. It is also possible to laminate a film, for example of rigid PVC, which has been provided with a veneer pattern, to the film material according to the invention. In this way, a surface coating which has substantially better scratch resistance than known comparable materials is obtained in every case.
The attached FIGURE explains the invention in relation to a laminate film. In this FIGURE, 10 represents a base layer of a film-forming plastic, 12 represents an adhesive layer and 14 represents a film according to the invention.
It can be seen that spheres (16) are incorporated in the layer (14), and in particular in such a way that the surfaces of the film according to the invention have a dome structure which is characterized in that the individual spheres (16) are enclosed by a continuous skin of the plastic matrix.
The films and sheets according to the invention are matted and at the same time more scratch-resistant. They can be easily embossed in fully portraying a desired structure, e.g., a wood-like structure, whereby the scratch-resistance and the mattness is surprisingly maintained.